Add workiq_send_channel_message tool for top-level channel posts

Summary

Add a workiq_send_channel_message tool for posting a top-level message to a Teams channel. Today the workiq surface can read channel messages and reply to existing threads, but it cannot start a new channel post — leaving a gap versus the chat surface, which has both workiq_send_chat_message and workiq_reply_to_chat_message.

Current channel tools

• workiq_list_channels — read
• workiq_list_channel_messages — read
• workiq_reply_to_channel_message — reply only

Missing: create a new top-level channel post.

Graph API

Supported and documented — no new permissions needed beyond what the existing reply tool already uses:

• POST /teams/{team-id}/channels/{channel-id}/messages
• Docs: https://learn.microsoft.com/en-us/graph/api/channel-post-messages?view=graph-rest-1.0
• Delegated permission: ChannelMessage.Send (least privileged)
• Request body: a chatMessage object; only body is required. Supports contentType: html|text, subject, importance, and mentions (same shape as chat message mentions).

Reply endpoint used by the existing workiq_reply_to_channel_message tool is a different route (.../messages/{id}/replies), so this is genuinely a separate capability.

Suggested tool shape

Mirror workiq_send_chat_message for consistency:

workiq_send_channel_message({
  teamId: string,           // required
  channelId: string,        // required
  content: string,          // required
  contentType?: "html" | "text",  // default "html"
  subject?: string,         // channel posts support a subject/title line
  importance?: "normal" | "high" | "urgent",
  mentions?: [ /* same shape as send_chat_message mentions */ ]
})

Returns the created chatMessage (id, webUrl, createdDateTime) so callers can link back to the post.

Motivating use case

I have a Copilot/Scout automation ("Post my Daily Summary") that runs on weekdays, reads my Obsidian daily note, and needs to post it to a Teams channel as a new top-level post — not as a reply to any existing thread. Without this tool the automation has to fall back to Playwright browser automation against teams.microsoft.com, which is fragile.

This is likely a common pattern for status updates, standups, release announcements, incident notifications, etc.

Nice-to-have follow-ups (out of scope for this ask, but related)

• Optional attachments / hostedContents support for images and file cards.
• A matching workiq_send_channel_announcement or messageType: "announcement" flag — announcement posts are a distinct channel message type that would be very useful for release/broadcast automations.

Start by locating the existing workiq_send_chat_message and workiq_reply_to_channel_message tools and compare their argument and response handling. Add the top-level channel-post capability using the documented Graph endpoint, then verify that required fields, optional message properties, and the created chatMessage response are supported.